In recent years, there has been proposed, as described in Patent Documents 1 to 4, for example, a metamaterial that artificially controls a dispersion relationship of an electromagnetic wave propagating in a structure by periodically arranging conductor patterns or conductor structures. For example, a metamaterial, which is controlled such that a wavelength of the electromagnetic wave is remarkably shortened, is used thereby to enable a resonator antenna to be reduced in size. Further, when a metamaterial structure that controls electromagnetic wave propagation in a certain frequency band (electromagnetic Band Gap: which will be denoted as EBG below) is used, an electromagnetic interference between circuits due to unwanted electromagnetic wave propagation from a high frequency circuit can be prevented.
For example, Patent Document 1 discloses therein a small-sized antenna structure utilizing a composite right and left handed (CRLH) line as one form of a metamaterial. A decode line in the antenna disclosed in Patent Document 1 is configured with periodically arranging unit cells each containing a conductor plane, a conductor patch arranged in parallel with the conductor plane, and a conductor via for connecting between the conductor plane and the conductor patch. Further, Patent Document 1 discloses therein that a conductor element is provided between the conductor plane and the conductor patch to increase a capacity between the adjacent conductor patches in order to be operated as a left handed medium at a lower frequency side. Furthermore, for a similar purpose, there is disclosed that a slit is provided near the connection part between the conductor plane and the conductor via to form a coplanar line, thereby increasing an inductance between the conductor plane and the conductor patch.
Additionally, Patent Document 2 discloses several EBG structures therein. For example, FIG. 4 illustrates cross-section configurations of a resonance via-type EBG structure and equivalent circuits per unit cell, respectively. FIGS. 1 and 2 illustrate top views of an inductive grid-type EBG structure, and FIG. 5 illustrates equivalent circuits per unit cell of the inductive grid type EBG structure, respectively.
Patent Document 3 discloses therein a uniplanar compact photonic bandgap structure (which will be called UC-PBG structure below) as one form of the inductive grid-type EBG structure. The UC-PBG structure is configured of two conductor layers, that is, a conductor layer which has a first conductor plane having no opening and a conductor layer having a periodical structure of a conductor pattern.
Patent Document 4 discloses therein an alternating impedance electromagnetic bandgap structure (which will be called AI-EBG structure below) as one form of the inductive grid type EBG structure. The AI-EBG structure is also configured of two conductor layers similar to the UC-PBG structure, that is, a conductor pattern layer having a periodical structure of the conductor pattern and a conductor plane layer having no opening. The conductor pattern layer is configured with an inductance element made of a large square conductor patch forming a periodical structure and a small square conductor patch connecting between adjacent large conductor patches as the layout shown in FIG. 1A in Patent Document 4. A small conductor patch and each large conductor patch, which function as an inductance element, are connected to an apex of the large conductor patch.